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A global biogeographic classification of the mesopelagic zone

The mesopelagic zone of the ocean, which is comprised of the 200 to 1000 m below the ocean surface, is poorly understood. Our limited scope of understanding for these areas may become increasingly problematic, as they may be vulnerable to global issues such as climate warming, deoxygenation, acidification, commercial fishing, and seabed mining.

A new paper published in Deep Sea Research Part I: Oceanographic Research Papers is co-authored by Nereus Program Principal Investigators Daniel Dunn and Patrick Halpin (Duke), and Fellow Gabriel Reygondeau (UBC), and provides a global biogeographic classification of the mesopelagic zone to reflect the regional scales over which the ocean interior varies in terms of biodiversity and function. It is based on current knowledge and available biotic and abiotic datasets on deep-pelagic ecosystems.

The classification presented in the paper acts as a ‘current state of knowledge’ framework which future data/analyses can be used to:
(1) refine boundary locations and dynamics as spatiotemporal information accumulates,
(2) investigate these dynamics to better understand the mechanisms underlying pelagic boundaries, and
(3) provide a guide to the regional scales over which the deep-pelagic ocean varies in terms of biodiversity and function, thereby informing global conservation efforts.

Additionally, the regions proposed here may be used as a foundation for a biogeographical framework in future studies to quantify potential anthropogenic impacts in deep-pelagic ecosystems.

Ultimately, the classification set forth in this paper will prove to be a useful and timely contribution to policy planning and management for conservation of deep-pelagic marine resources. Specifically, this research provides insights to the spatial scale at which faunal communities are expected to be largely similar in composition, and can thus inform application of ecosystem-baed management (EBM) approaches, marine spatial planning, and the distribution and spacing of networks of representative protected areas.

Abstract
We have developed a global biogeographic classification of the mesopelagic zone to reflect the regional scales over which the ocean interior varies in terms of biodiversity and function. An integrated approach was necessary, as global gaps in information and variable sampling methods preclude strictly statistical approaches. A panel combining expertise in oceanography, geospatial mapping, and deep-sea biology convened to collate expert opinion on the distributional patterns of pelagic fauna relative to environmental proxies (temperature, salinity, and dissolved oxygen at mesopelagic depths). An iterative Delphi Method integrating additional biological and physical data was used to classify biogeographic ecoregions and to identify the location of ecoregion boundaries or inter-regions gradients. We define 33 global mesopelagic ecoregions. Of these, 20 are oceanic while 13 are ‘distant neritic.’ While each is driven by a complex of controlling factors, the putative primary driver of each ecoregion was identified. While work remains to be done to produce a comprehensive and robust mesopelagic biogeography (i.e., reflecting temporal variation), we believe that the classification set forth in this study will prove to be a useful and timely input to policy planning and management for conservation of deep-pelagic marine resources. In particular, it gives an indication of the spatial scale at which faunal communities are expected to be broadly similar in composition, and hence can inform application of ecosystem-based management approaches, marine spatial planning and the distribution and spacing of networks of representative protected areas.

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The Nereus Program strives to explore a broad range of perspectives and scientific opinions on ocean sustainability, and to create an inclusive community of researchers and other marine professionals. This principle is founded on the Nippon Foundation’s vision of global capacity building to ensure that our oceans’ legacy is preserved and potential is protected for future generations.